Hi, bit late with answer but FS2004 works great on Windows 10.
Below is a guide I put together:
• First and most important under the assumption that your FS runs OK on your old PC. Copy your ENTIRE FS2004 folder from your old PC onto a separate hard drive! To copy my 36GB takes close to two hours!
• Second have the four original installation CD discs available!
• Finally, have your new W10 PC Note that I have no experience with installing FS2004 on the old rigs upgraded to W10! (Judging from the chat rooms there might be some issues with these)
Step by step procedure to install FS2004 on the new W10 PC:
• Load the four CD discs using either built in or external CD drive (I got a warning message from Microsoft – unknown origin (strange) – so have O.K.d the install. Install it (custom!) to your own folder on C drive, NOT to the Program Files, which I thing is a default. I named my folder FS2004.
• Answer NO at the end of install to run the FS, instead remove No 4 CD.
• Update the FS to v9.1. The update is available for the download in below link. It is an easy install placing the program file to your new FS folder and running it. https://flyawaysimulation.com/downloads/files/2795/flight-simulator-2004-update-v91/
• Get No CD Patch from below download. Again, an easy install to replace the fs9.exe file by the new downloaded file. https://flyawaysimulation.com/downloads/files/15244/microsoft-flight-simulator-2004-v91-no-cd-patch/
• Run FS (no need for the disc 4 installed, you got the patch!) and you find out that there is no aircraft preview in the opening screen just black field. It does not bother me because I can see and select the aircraft I want to fly in the drop-down. But if you want, hit ALT and ENTER and the aircraft picture appears. Test FS for basic functionality, take a quick flight with Cessna or similar.
• This is a good practice! Copy the entire contents of your newly installed FS folder to a back-up hard drive. (You can call it RAW FS9). It should have 2.69GB, so should not take long to copy. It is good to have the original files available!
Now to bring you newly created FS in W10 to the standard of your FS from former PC. Hook up to your W10 PC your external drive where you backed-up your FS folder. Delete all files from the following folders in your newly installed FS folder in your W10 PC, and copy in the corresponding files from your back-up hard drive into:
1. Addon Scenery folder, if you added or modified the scenery.
2. Aircraft folder, if you added or modified aircraft.
3. Effects folder, if you added or modified effects.
4. Gauges folder, if you added or modified gauges.
5. Modules folder, if you added or modified modules.
6. Scenery sub-folders folders (Afri, Asia, Aust, Eure, Eurw, Namc, Name, Namw, Ocen). This may not be necessary unless you modified some airport files or added flattens in your original FS. If you know where, just replace these files in given folders.
7. Scenery/World/Scenery folder. This is where your traffic files and altitude corrections are.
8. Sound folder, if you modified, added sounds or used Edit Voice pack.
9. Texture folder, if you modified or added textures.
10. Replace Scenery.cfg file in the main FS folder with the original back-up file! (This is important, so that you do not have to activate all your sceneries!) Note that the sceneries listed in this file should match the sceneries in your Addon Scenery folder otherwise you get a message if some sceneries are listed in Scenery.cfg file and are missing in the Addon folder!
Few advices or enhancing your FS2004, making it more realistic and mainly reduce those enjoying stutters (momentary screen freezes, apparently caused due to the old program running on the new higher capacity PC):
Get FS Environment 9 v1.3 from AVSIM Misc files library:
In this document are great enhancements available to make your FS more realistic and mainly! The FS9 Optimization section which changes some numbers in your Roaming FS9.cfg file (Located in your Windows 10 C drive/Users/Your Name/AppData/Roaming/Microsoft/FS9 folder). This greatly reduced my stutters. (Note that the TextureMaxLoad=10 needs to be added as a separate line! The creators of this great piece of info forgot to mention it,) Also to see your AppData file you need to set your files options to show the Hidden Files and Folders!
In general, you do not need to go for high FPS. I run at 25 FPS and the flights are nice and fluid. For info below are the settings I use. These give me great scenery and fluid flying (clearly, you might experiment with those):
Terrain Mash Complexity 100, Terrain Texture Size High, Terrain Detail Land Only, Water effects Low, Special Effects Detail Medium, Scenery Complexity Very Dense, Add-on Dynamic Scenery Unchecked, Ground Scenery Cast Shadows, Sun Glare and Lens Flare all Unchecked (these do not do too much and save capacity)
Global Aircraft Quality Low, Virtual Cockpit Gauge Quality High, In the rest only the Landing lights checked, rest unchecked.
Sight Distance 70 MI, Cloud Draw Distance 40 MI, 3D Cloud Percentage 50, Detailed Clouds Checked, Cloud Coverage Density High.
Target Frame Rate 25, Render to Texture Checked, Transform and Lightning Checked, Anti-Aliasing Unchecked. MIP Quality 4, Hardware Render Lights 6, Global Max Texture Size High.
Realism and Weather:
Rate at which weather changes over time Medium.
Additional note. Since I fly using the keyboard the F keys on my new laptop are active only when the FN key is pressed. This is enjoying because for example to handle flaps using F keys you need to hold the FN key as well, you can fix this by using the Assignments in Settings to change the Flaps from F keys to a single key on your new PC keyboard. I assigned “D” key to flaps down sequential and “T” key to flaps up sequential.